Response of the growth plate of uremic rats to human growth hormone and corticosteroids

Children with chronic renal failure in general present growth retardation that is aggravated by corticosteroids. We describe here the effects of methylprednisolone (MP) and recombinant human growth hormone (rhGH) on the growth plate (GP) of uremic rats. Uremia was induced by subtotal nephrectomy in 30-day-old rats, followed by 20 IU kg-1 day-1 rhGH (N = 7) or 3 mg kg-1 day-1 MP (N = 7) or 20 IU kg-1 day-1 rhGH + 3 mg kg-1 day-1 MP (N = 7) treatment for 10 days. Control rats with intact renal function were sham-operated and treated with 3 mg kg-1 day-1 MP (N = 7) or vehicle (N = 7). Uremic rats (N = 7) were used as untreated control animals. Structural alterations in the GP and the expression of anti-proliferating cell nuclear antigen (PCNA) and anti-insulin-like growth factor I (IGF-I) by epiphyseal chondrocytes were evaluated. Uremic MP rats displayed a reduction in the proliferative zone height (59.08 ± 4.54 vs 68.07 ± 7.5 æm, P < 0.05) and modifications in the microarchitecture of the GP. MP and uremia had an additive inhibitory effect on the proliferative activity of GP chondrocytes, lowering the expression of PCNA (19.48 ± 11.13 vs 68.64 ± 7.9 percent in control, P < 0.0005) and IGF-I (58.53 ± 0.96 vs 84.78 ± 2.93 percent in control, P < 0.0001), that was counteracted by rhGH. These findings suggest that in uremic rats rhGH therapy improves longitudinal growth by increasing IGF-I synthesis in the GP and by stimulating chondrocyte proliferation.

Insulin impairs the maturation of chondrocytes in vitro

The precise nature of hormones and growth factors directly responsible for cartilage maturation is still largely unclear. Since longitudinal bone growth occurs through endochondral bone formation, excess or deficiency of most hormones and growth factors strongly influences final adult height. The structure and composition of the cartilaginous extracellular matrix have a critical role in regulating the behavior of growth plate chondrocytes. Therefore, the maintenance of the three-dimensional cell-matrix interaction is necessary to study the influence of individual signaling molecules on chondrogenesis, cartilage maturation and calcification. To investigate the effects of insulin on both proliferation and induction of hypertrophy in chondrocytes in vitro we used high-density micromass cultures of chick embryonic limb mesenchymal cells. Culture medium was supplemented with 1 percent FCS + 60 ng/ml (0.01 æM) insulin and cultures were harvested at regular time points for later analysis. Proliferating cell nuclear antigen immunoreactivity was widely detected in insulin-treated cultures and persisted until day 21 and [ H]-thymidine uptake was highest on day 14. While apoptosis increased in control cultures as a function of culture time, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL)-labeled cells were markedly reduced in the presence of insulin. Type II collagen production, alkaline phosphatase activity and cell size were also lower in insulin-treated cultures. Our results indicate that under the influence of 60 ng/ml insulin, chick chondrocytes maintain their proliferative potential but do not become hypertrophic, suggesting that insulin can affect the regulation of chondrocyte maturation and hypertrophy, possibly through an antiapoptotic effect

Cytokine accumulation in osteitis fibrosa of renal osteodystrophy

Bone marrow fibrosis occurs in association with a number of pathological states. Despite the extensive fibrosis that sometimes characterizes renal osteodystrophy, little is known about the factors that contribute to marrow accumulation of fibrous tissue. Because circulating cytokines are elevated in uremia, possibly in response to elevated parathyroid hormone levels, we have examined bone biopsies from 21 patients with end-stage renal disease and secondary hyperparathyroidism. Bone sections were stained with antibodies to human interleukin-1alpha (IL-1alpha), IL-6, IL-11, tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-ß (TGF-ß) using an undecalcified plastic embedding method. Intense staining for IL-1alpha, IL-6, TNF-alpha and TGF-ß was evident within the fibrotic tissue of the bone marrow while minimal IL-11 was detected. The extent of cytokine deposition corresponded to the severity of fibrosis, suggesting their possible involvement in the local regulation of the fibrotic response. Because immunoreactive TGF-ß and IL-6 were also detected in osteoblasts and osteocytes, we conclude that selective cytokine accumulation may have a role in modulating bone and marrow cell function in parathyroid-mediated uremic bone disease

Hiperplasia de mastócitos na oxalose óssea / Incresead mast cell number in oxalosis of bone

Objetivos. Avaliar através de técnicas de hitomorfometria a incidência de hiperplasia de mastócitos na medula óssea de pacientes portadores de oxalose e insuficiência renal crônica. Material e Métodos. Foram estudados 18 indivíduos em 3 grupos: 6 (4 homens e 2 mulheres com média de idade de 26.31+2.5 anos) portadores de oxalose óssea e insuficiência renal crônica (IRC); 6 (5 mulheres e 1 homem com idade média de 22.1+3.56 anos) portadores de IRC e 6 indivíduos saudáveis (5 homens e 1 mulher com idade média de 23+2.78 anos). A análise do tecido ósseo foi realizada em biópsias de crista ilíaca, incluídas em resina, sem descalcificaçao prévia e coradas pela técnica do Azul de Toluidina. A contagem dos mastócitos foi feita utilizando-se sistema analisador de imagens e os valores (média+DP) foram expressos sob a forma de células por mm2 de tecido. Resultados. O número de mastócitos foi significativamente maior nos portadores de oxalose óssea, 32.67+9.59, ao comparar com os pacientes portadores de IRC sem oxalose (20.84+5.04, p<0.05) e nos indivíduos do grupo controle (3.26+1.03, p<0.001). Conclusoes. A oxalose óssea está associada com um aumento substancial do número de mastócitos na medula óssea. Esta alteraçao nao está relacionada com a IRC per se e nao parece representar uma resposta inespecífica à fibrose medular. O acúmulo anormal de mastócitos deve, de alguma forma, contribuir para o desenvolvimento da fibrose de medula óssea que acompanha esta condiçao.